[英]Scikitlearn - order of fit and predict inputs, does it matter?
剛開始使用這個庫...使用RandomForestClassifiers有一些問題(我已經閱讀過文檔,但沒有弄清楚)
我的問題非常簡單,比方說我有一個火車數據集
ABC
1 2 3
其中A是自變量(y),BC是因變量(x)。 假設測試集看起來相同,但順序是
BAC
1 2 3
當我調用forest.fit(train_data[0:,1:],train_data[0:,0])
然后我需要在運行之前重新排序測試集以匹配此順序嗎? (忽略我需要刪除已經預測的y值(a)的事實,所以讓我們說B和C亂序......)
是的,你需要重新排序它們。 想象一個更簡單的案例,線性回歸。 該算法將計算每個特征的權重,因此,例如,如果特征1不重要,則將為其分配接近0權重。
如果在預測時間順序不同,則一個重要特征將乘以這幾乎為零的權重,並且預測將完全關閉。
elyase是正確的。 scikit-learn
將以您給出的任何順序簡單地獲取數據。 因此,您必須確保在訓練和預測時間內數據的順序相同。
這是一個簡單的說明示例:
訓練時間:
from sklearn.tree import DecisionTreeClassifier
model = DecisionTreeClassifier()
x = pd.DataFrame({
'feature_1': [0, 0, 1, 1],
'feature_2': [0, 1, 0, 1]
})
y = [0, 0, 1, 1]
model.fit(x, y)
# we now have a model that
# (i) predicts 0 when x = [0, 0] or [0, 1], and
# (ii) predicts 1 when x = [1, 0] or [1, 1]
預測時間:
# positive example
http_request_payload = {
'feature_1': 0,
'feature_2': 1
}
input_features = pd.DataFrame([http_request_payload])
model.predict(input_features) # this returns 0, as expected
# negative example
http_request_payload = {
'feature_2': 1, # notice that the order is jumbled up
'feature_1': 0
}
input_features = pd.DataFrame([http_request_payload])
model.predict(input_features) # this returns 1, when it should have returned 0.
# scikit-learn doesn't care about the key-value mapping of the features.
# it simply vectorizes the dataframe in whatever order it comes in.
這是我在訓練期間緩存列順序的方式,以便我可以在預測時間內使用它。
# training
x = pd.DataFrame([...])
column_order = x.columns
model = SomeModel().fit(x, y) # train model
# save the things that we need at prediction time. you can also use pickle if you don't want to pip install joblib
import joblib
joblib.dump(model, 'my_model.joblib')
joblib.dump(column_order, 'column_order.txt')
# load the artifacts from disk
model = joblib.load('linear_model.joblib')
column_order = joblib.load('column_order.txt')
# imaginary http request payload
request_payload = { 'feature_1': ..., 'feature_1': ... }
# create empty dataframe with the right shape and order (using column_order)
input_features = pd.DataFrame([], columns=column_order)
input_features = input_features.append(request_payload, ignore_index=True)
input_features = input_features.fillna(0) # handle any missing data however you like
model.predict(input_features.values.tolist())
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